The use of seismic data to analyze subsurface geological structures, such as faults or other stratographic features, is relevant to interpreters searching for subsurface mineral and hydrocarbon deposits.
The acquisition of seismic data is typically accomplished by transmitting an acoustic signal into the earth and recording reflections of the signal. The layers of rock within the earth differ in their acoustic properties and these changes in properties produce reflections of the seismic signal. Data acquisition therefore, involves energy sources generating signals propagating into the earth and reflecting from subsurface geological structures. The reflected signals are recorded by receivers on or near the surface of the earth. The reflected signals are stored as time series (pre-stack seismic traces) that consist of amplitudes of acoustic energy, which vary as a function of time, receiver position and source position. Because subsurface geological structures are different, depending on formation layers within the earth, the variation in the amplitudes of the reflected acoustic signals are indicative of the physical properties of these structures from which the signals reflect.
The seismic data are generally processed to create acoustic images from which data interpreters may create images of the subsurface formations. Data processing therefore, involves procedures that vary depending on the nature of the seismic data acquired and the geological structure being interpreted. A single echo (reflection) train is usually called a seismic trace. A seismic trace generally represents a combination of many sinusoidal waves as a function of time. The strength of the recorded reflections rises and falls over a period of several seconds, and is recorded in digital form or converted to digital form for processing and analysis. The variations in the seismic trace generally consist of amplitude characteristics such as peaks, zero crossings and troughs.
A collection of seismic traces (known as pre-stack gathers) may be stacked (processed) to form an image referred to as post-stack seismic data. Both pre-stack and post-stack seismic data images may be interpreted in a variety of different ways to ascertain the nature of the sub-surface geological structures being investigated for mineral and hydrocarbon deposits. However, the differences in data format and display between pre-stack and post-stack seismic data images force these interpretations, and any further related processing, to be largely independent of one another.
An example of this limited linking between pre-stack and post-stack seismic data is provided by Paul Hatchell in his paper “Fault whispers: Transmission distortions on pre-stack seismic reflection data,” which is incorporated herein by reference and illustrated in FIG. 8. A series of normal move out (NMO)-corrected migrated common mid-point (CMP) gathers from one in-line location are illustrated on the left side of FIG. 8. For each NMO-corrected migrated CMP gather at a respective cross-line location, a corresponding feature plot is derived (maximum trough amplitudes for each event versus offset) and illustrated on the right side of FIG. 8. Although amplitude and time distortions that move systematically with cross-line position are evident from this type of analysis and display, this type of display does not allow the correlation of such distortion patterns with any related post-stack seismic data or further processing and analysis of the same using post stack techniques.